This invention relates to a process for purification of a styrene polymer, more particularly, it relates to a process for purifying a styrene polymer having a high degree of syndiotacticity in stereochemical structure of polymer chain with good efficiency and high purity. 2. Description of the Related Arts
Heretofore, a styrene polymer produced by the radical polymerization method has an atactic configuration in stereochemical structure, and it has been molded into various shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding, cast molding, etc., and has widely been used for domestic electric appliances, office machines, household articles, packaging containers, toys, furnitures, synthetic papers, other industrial materials, etc.
However, the styrene polymer having atactic configuration has problems that it is inferior in heat resistance and chemical resistance.
The group of the present inventors have previously succeeded in developing a styrene polymer having a high degree of syndiotacticity, and further shown that a styrene polymer having syndiotactic configuration can be obtained by using a catalyst comprising a contacted product (alkylaluminoxane) of a transition metal compound and an organic aluminum compound with a condensing agent (Japanese Patent Application Laid-Open No. 187708/1987, No. 179906/1988 and No. 241009/1988).
According to the above methods, deashing and washing are each carried out by using a mixed solution of hydrochloric acid and methanol. However, when the deashing and washing are carried out with the mixed solution of hydrochloric acid and methanol, an acid-resistant equipment is required as an equipment for washing so that special steel or a tank subjected to glass lining must be used whereby the problem that costs of equipments become expensive is present.
Also, in the polymer product obtained by washing with the mixed solution of hydrochloric acid and methanol, a minute amount of a halogen compound is present so that it causes the problem of occurring mold corrosion, or coloring to black when a heat resistant test for a long period of term is carried out. Further, when the catalytic component contains halogen, the halogen reacts with an alcohol to form a corrosive component such as hydrochloric acid so that it is not preferred.
While the styrene polymer having a syndiotactic configuration can be produced by a slurry polymerization, a bulk polymerization, etc., it is advantageous to effect the polymerization with high content of styrene in view of the points of catalyst activity and productivity. Also, it has been desired to decrease the catalytic component remained in the resulting polymer product by deashing.
However, in a polymer product which is low in a conversion rate or polymerized by making low styrene concentration, deashing can be easily effected, but in the case of a polymer product with a high conversion rate of 60% or more, there is the problem that deashing and washing thereafter become difficult with increase of the conversion rate.
The present inventors have proceeded with consideration from such a point of view and investigated intensive studies to develop a process which can effect deashing (removal of residual catalyst) of a styrene polymer which is a high conversion rate effectively and can purify it to high purity.